Tiny boring bar?

I want to drill a hole in the centre of a workpiece which has been one-stop machined in a lathe, ie only chucked once so everything is concentric and nice.

I have centre drills, drills and reamers, but I want it to be dead-centre, which it won't be if I use those.

I thought a boring bar would do the job - but the hole is only 4 mm diameter.

Anyone know where I can get a suitable tiny boring bar?

Anyone got any better ideas?


Reply to
Peter Fairbrother
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  1. How long's the hole ?
  2. What's the material ?
  3. How are you going to get the swarf out ? (See 2)



Reply to

Peter Fairbrother said

Has to be the best way Peter but it will depend how deep the hole is.

I have a similar issue at times and have bored 5mm x 22mm using a 9mm sq HSS tool-bit ground away leaving a 3mm wide tip and about 4mm body, having first drilled out to 4mm. I'm sure you could do even better with a 3mm dia HSS tool-bit with the body ground away to (say) 2.5mm for clearance. If you drill out to 3mm first you are only going to be taking

0.005 or 0.010mm cuts anyway so there shouldn't be an issue of bending.

How you hold the tool-bit could be an issue but not to a man of your experience.


Reply to

Just under 6mm deep.

The hole goes all the way through.

304 stainless for now, later 316L stainless and Inconels, maybe even something more exotic.

I don't follow.

I planned to drill a small through hole and then expand it with a boring bar, if I can get one that size - but I am open to other ideas.

It's an open ended hole, sort-of: a bit of 18 mm diameter scrap steel tube is mounted directly on the lathe spindle, faced off, and 6mm/8mm thick sheet blanks about 50 mm square are silver soldered to it for turning. They get made round and faced, then turned to shape, largest final diameter is 41mm.

I'm making small turbine wheels and guide vanes. The hole is cut, then the blades. Part.

To turn the back face I plan to use the hole to fit the seperated piece on a turned-in-place shaft. Accuracy is needed, and extreme concentrencity (sp?) of the hole is essential.

The holes will later be reamed out to final size, some will take shafts. The precise initial size of the hole doesn't matter - it has to be accurately perpendicular to the turned face, and accurately concentric, but that's all.

Reply to
Peter Fairbrother

Sounds like a job for a fixed steady

Ian Phillips

Reply to
Ian Phillips

On my little Atlas, the boring bar holder accepts 1/2" round bars with sleeves for 3/16" 1/4" and 3/8". When I needed a 1/8"(.125") boring bar, I grabbed a piece of 1/4" dia. drill rod, turned down about an inch of it to .100", then ground a cutting end I could live with. Then hardened and honed the cutting end. You can also use a good quality bolt and do the same thing if you are fresh out of drill rod.

Alternatively, sacrifice a 3mm drill bit and gr>

Reply to

Suitably mounted, disposable milling cutters or slot drills make excellent small diameter boring bars. No regrinding needed - you already have several ready sharpened teeth. Just pick a size about 75% of final hole size.

For really tough jobs use a carbide end mill - they're stiffer than any conventional boring bar of similar size.


Reply to

Look at item 13 on

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which is a solid carbide boring bar for holes from 3mm dia and up to 32mm deep at £2.00 each. Have not bought of him for a couple of years but what I did buy was excellent.

Dick Gays, Leicester, UK.

Reply to
Dick Gays

That's the place I was trying to think of. I bought a couple of them a few years ago -never had to use them, but thought they would be worth the money in case I ever needed them. They look great, and being carbide I'd expect them to cut well. Have never seen boring bars so small.



Reply to
Kevin Steele

I bought some of those miniature carbide boring bars a while back and have been pleased with them. I have a vague memory that he no longer imports these Russian tools, but I may be wrong.

Cliff Coggin Kent UK

Reply to
Cliff Coggin


IFANGER (Swiss) make really nice *tiny* HSS boring bars.

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Click on English, then the Microturn icon, then 'More Product Info', and get a 20-page pdf catalogue. It's good, but not cheap. There's bound to be a uk distributor.


Peter Fairbrother wrote:

Reply to

I know this is shutting the stable door-type advice, but would it b

easier to start again, accurately ream the hole, mount it on a tigh mandrel and then repeat the machining holding the mandrel in collet/chuck. That way all should be concentric to the hole

-- Myford Mat

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Reply to
Myford Matt

I might do some future ones that way.

What I did was go to work on a cheap-ish TC tipped "masonry" drill with a Dremel and a diamond wheel. The TC tip overhangs the shaft anyway, so you don't have to work the shaft. Works great.

Reply to
Peter Fairbrother

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